Aha, where is he planning on wearing this costume, if I may ask? Conventions, in my experience, are nothing if not open minded places. Cosplayers are people of all ages, sizes, genders, races, etc., and most of them are considerate enough to ignore these factors in favor of appreciating the costume's construction and sharing the love of the character and his/her/their origin. Crossdressing is quite prevalent as well, and I really can't imagine anyone bringing it up in a negative fashion.